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Structural evolution of the Louisiana gulf coast
The salt tectonics off the Louisiana gulf coast can be explained through two possible methods. The first method attributes spreading of the salt because of sedimentary loading while the second method points to slope instability as the primary cause of gliding of the salt. The first method results in the formation of growth faults in the overlying sediment.〔 Growth faults are normal faults that occur simultaneously with sedimentation, causing them to have thicker sediment layers on the downthrown sides of the faults. In the second method both the salt and the sediment are moving, making it more likely to migrate.〔
==General Features of the Gulf of Mexico==
The Gulf of Mexico is tectonically passive with low shear strength, but seaward slumping has produced a weak but mappable stress field. The stress map shows that in offshore Louisiana, maximum horizontal stress is oriented parallel to the shelf. Characteristics of the clastic sedimentary wedge have the greatest influence on the local stresses. Topography, lithology, and faults also affect how the stress map appears, but impermeable salt structures are significant because they resist movement.〔 Basement tectonic control cannot readily affect the stress map since the salt's weak surface does not easily transmit stress.〔
The observation of minibasins (small sedimentary basins) and other features have suggested that the salt in the Gulf of Mexico primarily moves by spreading under differential sedimentary loading, which needs many conditions (e.g. huge amounts of deposited material above the salt) to be met.〔 However, models and observation of the northern Gulf of Mexico favor gliding via slope instability. Controversies such as this example indicate that this area is structurally complicated.〔
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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